Drive transmission mechanism and drive transmission mechanism for printer apparatus

ABSTRACT

It is a drive transmission mechanism for a printer apparatus, which has a conveying roller gear connected to a conveying roller, an intermediate gear including a small-diameter intermediate gear portion for rotating the conveying roller gear, and an intermediate gear supporting shaft rotatably supporting a shaft insertion hole of the intermediate gear. In this mechanism, the conveying roller gear includes a conveying roller gear circular portion having a diameter that is substantially equal to the reference pitch circle diameter of the conveying roller gear. The intermediate gear includes a small-diameter intermediate gear circular portion having a diameter that is substantially equal to the reference pitch circle diameter of a small-diameter intermediate gear portion. Further, the intermediate supporting shaft is mounted therein in such a manner as to provide a predetermined fitting clearance between the intermediate supporting shaft and the shaft insertion hole.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a drive transmission mechanism, and to a drive transmission mechanism for a printer apparatus. More particularly, the invention relates to a drive transmission mechanism having plural gears, and to a drive transmission mechanism for a printer apparatus.

2. Description of the Related Art

Hitherto, there has been known a drive transmission mechanism for transmitting a driving force in a printer and so on by plural gears (see, for example, JP-A-5-014787).

JP-A-5-014787 discloses a printer apparatus provided with intermediate gears formed between a driving-side gear and a platen-roller-side gear by combining large and small, two gears, which are eccentric to a similar degree, with each other so that the directions of eccentricity thereof are opposite to each other on either side of a shaft thereof. The structure disclosed in JP-A-5-014787 reduces unevenness in the rotational speed thereof by disposing the large and small, two gears so that the unevennesses in the rotational speed due to the eccentricity each of these gears are cancelled out each other.

FIG. 16 is a perspective view showing a conventional thermal transfer printer. FIGS. 17 to 19 are views showing a drive transmission mechanism of the conventional thermal transfer printer shown in FIG. 16. The structure of the conventional thermal printer 100 is described hereinbelow by referring to FIGS. 16 to 19.

As shown in FIG. 16, the conventional thermal printer 100 has a metallic frame 110, a thermal transfer film accommodating member 111, a sheet feeding roller 112, a motor bracket 114 to which a motor 113 is attached, a film take-up member 115, a sheet feeding roller gear 116, plural intermediate gears 117, a metallic conveying roller 120, a resin conveying roller gear 130 connected to an end portion of the conveying roller 120, and a resin intermediate gear 140 for rotating the conveying roller gear 130. Further, as shown in FIGS. 17 to 19, the conventional thermal transfer printer 100 has a resin drive transmission gear 150, which is connected to a drive shaft 113 a of the motor 113, for rotating the intermediate gear 140, and an intermediate gear support shaft 160 rotatably supporting the intermediate gear 140. As shown in FIG. 16, the frame 110 is U-shaped. The thermal transfer film accommodating member 111 and the sheet feeding roller 112 are disposed on the inner surface side of the frame 110. Moreover, the motor 113 transmits a driving force to the drive transmission gear 150 through the drive shaft 113 a of the motor 113. Furthermore, the motor bracket 114 is mounted on the outer surface of the frame 110. Additionally, the film take-up member 115, the sheet feeding roller gear 116, and the plural intermediate gears 117 are placed between the frame 110 and the motor bracket 114. These plural intermediate gears 117 are placed so that the film take-up member 115 and the sheet feeding roller gear 116 can be driven by the single motor 113.

Further, as shown in FIGS. 16 and 19, the conveying roller 120 is disposed under the thermal transfer film accommodating member 111 on the inner surface side of the frame 110, and rotatably mounted on the frame 110 by a bearing 118. As shown in FIGS. 17 and 19, a D-cut part 121 is formed in an end portion of this conveying roller 120 by performing a cutting work operation or the like. Furthermore, a D-shaped through hole 131, through which the D-cut part 121 of the conveying roller 120 is inserted, is formed in the conveying roller gear 130. The intermediate gear 140 has a circular shaft insertion hole 141. Moreover, as shown in FIG. 17, the intermediate gear 140 includes a small-diameter intermediate gear portion 142, which meshes with the conveying roller gear 130, and a large-diameter intermediate gear portion 143 that meshes with the drive transmission gear 150 and that has a diameter, which is larger than that of the small diameter intermediate gear portion 142. Furthermore, as shown in FIG. 19, the intermediate gear supporting shaft 160 includes an attaching portion 161 fixedly attached to the frame 110 by performing a caulking operation or the like. Additionally, as shown in FIGS. 17 to 19, the intermediate gear supporting shaft 160 has a circular shape, which is substantially the same as that of the shaft insertion hole 141.

Next, a drive transmission operation of the conventional thermal transfer printer 100 is described hereinbelow by referring to FIG. 17. First, a driving force of the motor 113 (see FIG. 16) is transmitted to the drive transmission gear 150 through the drive shaft 113 a of the motor 113. Thus, the drive transmission gear 150 rotates in the direction of an arrow M shown in FIG. 17. Subsequently, the driving force of the drive transmission gear 150 is transmitted to the large-diameter intermediate gear portion 143 of the intermediate gears 140. Thus, the large-diameter intermediate gear portion 143 and the small-diameter intermediate gear portion 142 rotate in the direction of an arrow N shown in FIG. 17. Then, the driving force of the small-diameter intermediate gear portion 142 is transmitted to the conveying roller gear 130. Thus, the conveying roller gear 130 rotates in the direction of an arrow O shown in FIG. 17. Consequently, the driving force is transmitted to the conveying roller 120 through the D-cut part 121 of the conveying roller 120, which is inserted into the D-shaped through hole 131 of the conveying roller gear 130. Thus, the conveying roller 120 rotates.

In the conventional thermal transfer printer 100 shown in FIGS. 16 to 19, at least one of the conveying roller gear 130, the small-diameter intermediate gear portion 142, the large-diameter intermediate gear portion 143, and the drive transmission gear 150 may be eccentric due to manufacturing errors of the device, to abrasion caused after use of the device, and to thermal deformation thereof. In this case, it is difficult for the eccentric gear to be in contact with the adjacent gear so that an eccentric-gear-side part, whose diameter is equal to a reference pitch circle diameter of the eccentric gear, is brought into contact with an adjacent-gear-side part, whose diameter is equal to a reference pitch circle diameter of the adjacent gear. Thus, when the gears are driven, unevenness in the rotation of each of the gears occurs. Consequently, this conventional printer has a problem in that it is difficult to rotate the conveying roller gear 130 (or the conveying roller 120) at a constant rotational speed.

Further, the structure disclosed in JP-A-5-014787 is enabled to reduce unevenness in the rotational speed of a platen-roller-side gear in a case where an eccentric gear is used in a manufacturing stage (a stage in which the device is not used yet). Consequently, this conventional printer has a problem in that it is difficult to reduce the rotational speed of the platen-roller-side gear in a case where the gear becomes eccentric during the device is used.

Thus, hitherto, to solve the problems, there has been proposed a structure enabled to rotate a conveying roller gear (or the conveying roller) at a constant rotational speed without causing unevenness in the rotation of the gear (see JP-A-10-123785).

JP-A-10-123785 discloses an image forming apparatus provided with annular stopper members, which have a reference pitch circle diameter being equal to those of a swinging gear and a transfer roller gear and are coaxially connected to the swinging gear and the transfer roller gear, in a drive transmission structure in which a driving force from a photoconductive drum gear is transmitted to a transfer roller gear (or a conveying roller gear) through the swinging gear pushed in the direction of the transfer roller gear. The structure disclosed in JP-A-10-123785 prevents occurrences of unevenness in the rotational speed of the transfer roller by keeping the distance between the swinging gear and the transfer roller gear at a constant value through the use of the stopper members even when the distance between the centers of the photoconductive drum and the transfer roller changes.

However, the structure disclosed in JP-A-10-123785 has a problem in that because a coupler, the spring and the idler gear are needed for enabling the swinging gear, which is used for transmitting the driving force from the photosensitive drum gear to the transfer roller gear (or the conveying roller gear), to swing, the number of components increases for that. Also, this conventional structure has a problem in that because annular stopper members each having a reference pitch circle diameter, which is equal to those of the swinging gear and the transfer roller gear, are separately provided therein, the number of components increases in this regard. Additionally, this conventional structure has a problem in that because no stopper members are provided between the idler gear and the swinging gear and between the idler gear and the photosensitive drum gear, unevenness in the rotation is caused therebetween.

SUMMARY OF THE INVENTION

The invention is accomplished to solve the aforementioned problems. Accordingly, an object of the invention is to provide a drive transmission mechanism for a printer apparatus or the like, which is enabled to rotate a gear, which transmits a driving force, at a constant rotational speed without increasing the number of components.

According to a first aspect of the invention, there is provided a drive transmission mechanism for a printer apparatus, which has a metallic conveying roller for conveying sheets, a resin conveying roller gear connected to one end portion of the conveying roller, a resin intermediate gear, provided with a shaft insertion hole, for rotating the conveying roller, a resin drive transmission gear, mounted on a drive shaft of a motor, for rotating the intermediate gear as the motor is driven, and an intermediate gear supporting shaft for rotatably supporting the shaft insertion hole of the intermediate gear. The intermediate gear includes a first-side intermediate gear portion meshed with the conveying roller gear, and also includes a second-side intermediate portion meshed with the drive transmission gear. The intermediate gear is disposed in a position, in which the intermediate gear is caused by a load of the conveying roller to bite into the conveying roller gear and the drive transmission gear, when the gears are driven. The resin conveying roller gear includes a conveying roller gear circular portion that is provided integrally with the conveying roller gear and that has a diameter being substantially equal to a reference pitch circle diameter of the conveying roller gear. The resin drive transmission gear includes a drive transmission gear circular portion that is provided integrally with the drive transmission gear and that has a diameter being substantially equal to a reference pitch circle diameter of the drive transmission gear. The resin intermediate gear further includes a first-side intermediate gear circular portion, which is provided integrally with the drive transmission gear and has a diameter being substantially equal to a reference pitch circle diameter of the first-side intermediate gear portion, and also includes a second-side intermediate gear circular portion that is provided integrally with the intermediate gear portion and that has a diameter being substantially equal to a reference pitch circle diameter of the second-side intermediate gear portion. The intermediate gear supporting shaft is mounted in the shaft insertion hole of the intermediate gear in such a way as to provide a predetermined fitting clearance between the intermediate gear supporting shaft and the shaft insertion hole. The conveying roller gear circular portion is disposed in such a way as to be in contact with the first-side intermediate gear circular portion when the gears are driven. The drive transmission gear circular portion is disposed in such a manner as to be in contact with the second-side intermediate gear circular portion when the gears are driven.

As described above, in the drive transmission mechanism for a printer apparatus according to the first aspect of the invention, the conveying roller gear circular portion having a diameter being substantially equal to the reference pitch circle diameter of the conveying roller gear is provided at the conveying roller gear. Moreover, the first-side intermediate gear circular portion having a diameter being substantially equal to the reference pitch circle diameter of the first-side intermediate gear portion of the intermediate gear is provided at the first-side intermediate gear portion of the intermediate gear for rotating the conveying roller gear. Thus, when the gears are driven, the conveying roller gear circular portion and the first-side intermediate gear circular portion are in contact with each other. Consequently, the conveying roller gear and the first-side intermediate gear portion of the intermediate gear can be meshed with each other so that a conveying-roller-gear-side part, whose diameter is equal to the reference pitch circle diameter the conveying roller gear, is in contact with a first-side-intermediate-gear-portion-side part, whose diameter is equal to the reference pitch circle diameter of the first-side intermediate gear portion. Thus, even when at least one of the conveying roller gear and the first-side intermediate gear portion of the intermediate gear is eccentric, each of the conveying roller gear and the intermediate gear can be rotated at a constant rotational speed without causing unevenness in the rotation thereof. Furthermore, the second-side intermediate gear circular portion having a diameter being substantially equal to the reference pitch circle diameter of the second-side intermediate gear portion of the intermediate gear is provided at the second-side intermediate gear portion of the intermediate gear. Moreover, the drive transmission gear circular portion having a diameter being substantially equal to the reference pitch circle diameter of the drive transmission gear is provided at the drive transmission gear for rotating the intermediate gear. Thus, when the gears are driven, the second-side intermediate gear portion of the intermediate gear and the drive transmission gear are in contact with each other. Consequently, the second-side intermediate gear portion of the intermediate gear and the drive transmission gear can be meshed with each other so that a second-side-intermediate-gear-portion-side part, whose diameter is equal to the reference pitch circle diameter of the second-side intermediate gear portion, is in contact with a drive-transmission-gear-side part, whose diameter is equal to the reference pitch circle diameter of the drive transmission gear. Thus, even when at least one of the second-side intermediate gear portion and the drive transmission gear is eccentric, each of the intermediate gear and the drive transmission gear can be rotated at a constant rotational speed without causing unevenness in the rotation thereof. Further, the conveying roller gear circular portion is provided integrally with the conveying roller gear, while the first-side intermediate gear circular portion is provided integrally with the first-side intermediate gear portion of the intermediate gear. Thus, even in a case where the conveying roller gear circular portion and the first-side intermediate gear circular portion are provided in the mechanism, the number of components does not increase. Consequently, each of the conveying roller gear and the intermediate gear can be rotated at a constant rotational speed without increasing the number of components. Additionally, the second-side intermediate gear circular portion is provided integrally with the second-side intermediate gear portion of the intermediate gear, while the drive transmission gear circular portion is provided integrally with the drive transmission gear. Thus, even in a case where the second-side intermediate gear circular portion and the drive transmission gear circular portion are provided in the mechanism, the number of components does not increase. Consequently, each of the intermediate gear and the drive transmission gear can be rotated at a constant rotational speed without increasing the number of components. Besides, the intermediate gear supporting shaft is mounted in the shaft insertion hole of the intermediate gear in such a way as to provide a predetermined fitting clearance between the intermediate gear supporting shaft and the shaft insertion hole. Thus, when the gears are driven, the intermediate gear can easily be moved in such a manner as to bite into the conveying roller gear and the drive transmission gear. Thus, the conveying roller gear circular portion can surely be in contact with the second-side intermediate gear circular portion, while the first-side intermediate gear circular potion can surely be in contact with the drive transmission gear circular portion. Consequently, without separately providing a mechanism for swinging (or moving) the intermediate gear in the transmission mechanism, the conveying roller gear can surely be meshed with the intermediate gear, while the intermediate gear can surely be meshed with the drive transmission gear so that a conveying-roller-gear-side part, whose diameter is equal to the reference pitch circle diameter of the conveying roller gear, is in contact with an intermediate-gear-side part, whose diameter is equal to the reference pitch circle diameter of the intermediate gear, and that the intermediate-gear-side part, whose diameter is equal to the reference pitch circle diameter of the intermediate gear, is in contact with a drive-transmission-gear-side part, whose diameter is equal to the reference pitch circle diameter of the drive transmission gear. Furthermore, correction for unevenness in the rotation is performed on the engagement between the drive transmission gear and the intermediate gear, in addition to the engagement between the intermediate gear and the conveying roller gear. Thus, the unevenness in the rotation, which is caused at the drive transmission gear, is corrected at two places. Thus, as compared with a case in which such unevenness in the rotation is corrected at one place, the conveying roller gear can more surely be rotated at a constant rotational speed.

According to a second aspect of the invention, there is provided a drive transmission mechanism that includes a first gear and a second gear having a second first-side gear portion for rotating the first gear. The first gear includes a first circular portion that is provided integrally with the first gear and that has a diameter being substantially equal to a reference pitch circle diameter of the first gear. The second gear includes a second first-side circular portion that is provided integrally with the second first-side gear portion and that has a diameter being substantially equal to a reference pitch circle diameter of the second first-side gear portion. The first circular portion is disposed in such a way as to be in contact with the second first-side circular portion when the gears are driven.

As described above, in the drive transmission mechanism according to the second aspect of the invention, the first circular portion having a diameter being substantially equal to the reference pitch circle diameter of the first gear is provided on the first gear. Also, the second first-side circular portion having a diameter being substantially equal to the reference pitch circle diameter of the second first-side gear portion is provided at the second first-side gear portion for rotating the first gear. Thus, when the gears are driven, the first circular portion and the second first-side circular portion are in contact with each other. Consequently, the first gear and the second first-side gear portion of the second gear can be meshed with each other so that a first-gear-side part, whose diameter is equal to the reference pitch circle diameter of the first gear, is in contact with a second-first-side-gear-portion-side part, whose diameter is equal to the reference pitch circle diameter of the second first-side gear portion. Thus, even when at least one of the first gear and the second gear is eccentric, each of the first gear and the second gear can be rotated at a constant rotational speed without causing unevenness in the rotation thereof. Further, even in a case where the first circular potion is provided integrally with the first gear and where second first-side circular portion is provided integrally with the second first-side gear portion of the second gear to thereby provide the first circular portion and the second first-side circular portion in the mechanism, the number of components does not increase. Consequently, each of the first gear and the second gear can be rotated at a constant rotational speed without increasing the number of components.

Preferably, the drive transmission mechanism according to the second aspect of the invention is adapted so that the second gear has a shaft insertion hole, and further includes a second gear supporting shaft mounted in such a manner as to rotatably support the shaft insertion hole and as to provide a predetermined fitting clearance between the second gear supporting shaft and the shaft insertion hole. With such a configuration, when the gears are driven, the second gear can easily be moved in such a way as to bite into the first gear. Thus, the first circular portion and the second first-side circular portion can surely be in contact with each other. Consequently, the first gear and the second gear can mesh with each other, without separately being provided with a mechanism for swinging (or moving), so that a first-gear-side part, whose diameter is equal to a reference pitch circle diameter of the first gear, is in contact with a second-gear-side part, whose diameter is equal to a reference pitch circle diameter of the second gear.

Preferably, the drive transmission mechanism according to the second aspect of the invention further includes a third gear for rotating the second gear. The second gear further includes a second second-side gear portion meshed with the third gear, and also includes a second second-side circular portion that is provided integrally with the second second-side gear portion and that has a diameter being substantially equal to a reference pitch circle diameter of the second second-side gear portion. The third gear includes a third circular portion that is provided integrally with the third gear and that has a diameter being substantially equal to a reference pitch circle diameter of the third gear. The second second-side circular portion is disposed in such a manner as to be in contact with the third circular portion when the gears are driven. With such a configuration, when the gears are driven, the third circular portion and the second second-side circular portion are in contacted with each other. Thus, the third gear and the second second-side gear portion of the second gear can be meshed with each other so that a third-gear-side part, whose diameter is equal to a reference pitch circle diameter of the third gear, is in contact with a second-second-side-gear-portion-side part, whose diameter is equal to a reference pitch circle diameter of the second second-side gear portion. Consequently, even when at least one of the third gear and the second gear is eccentric, each of the third gear and the second gear can be rotated at a constant rotational speed without causing unevenness in the rotation thereof. Further, even in a case where the third circular portion is provided integrally with the third gear and where the second second-side circular portion are provided integrally with the second second-side gear portion of the second gear to thereby provide the third circular portion and the second second-circular portion in the mechanism, the number of components does not increase. Consequently, the third gear and the second second-side gear portion can be rotated at a constant rotational speed without increasing the number of components. Moreover, unevenness in the rotation, which occurs at the upstream side of driving-force transmission from the third gear, can be corrected at two places by providing the third circular portion at the third gear for rotating the second gear and also providing the second second-side circular portion at the second second-side gear portion included in the second gear. Thus, as compared with a case where such unevenness in the rotation is corrected at one place, the first gear can more surely be rotated at a constant rotational speed.

A printer apparatus according to the invention may include at least one of the drive transmission mechanisms according to the second aspect of the invention. With such a configuration, the gear included in the apparatus can be rotated at a constant rotational speed without increasing the number of components and without causing unevenness in the rotation thereof. Consequently, the apparatus of the invention can obtain an advantage of reducing unevenness in printing images on sheets, without increasing the number of components.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of this invention will become more fully apparent from the following detailed description taken with the accompanying drawings in which:

FIG. 1 is a perspective view illustrating a thermal transfer printer according to a first embodiment of the invention;

FIG. 2 is a side view illustrating a drive transmission mechanism of the thermal transfer printer according to the first embodiment of the invention, which is shown in FIG. 1;

FIG. 3 is a top view illustrating the drive transmission mechanism of the thermal transfer printer according to the first embodiment of the invention, which is shown in FIG. 1;

FIG. 4 is a cross-sectional view taken along line 200-200 in FIG. 2;

FIG. 5 is a side view illustrating the drive transmission mechanism of the thermal transfer printer according to the first embodiment of the invention, which is shown in FIG. 2, at the time of driving the printer;

FIG. 6 is a top view illustrating the drive transmission mechanism of the thermal transfer printer according to the first embodiment of the invention, which is shown in FIG. 3, at the time of driving the printer;

FIG. 7 is a cross-sectional view taken along line 300-300 in FIG. 5;

FIG. 8 is a cross-sectional view taken along line 400-400 in FIG. 5;

FIG. 9 is a side view illustrating a drive transmission mechanism of a thermal transfer printer according to a second embodiment of the invention;

FIG. 10 is a top view illustrating the drive transmission mechanism of a thermal transfer printer according to the second embodiment of the invention;

FIG. 11 is a cross-sectional view taken along line 500-500 in FIG. 9;

FIG. 12 is a side view illustrating the drive transmission mechanism of the thermal transfer printer according to the second embodiment of the invention, which is shown in FIG. 9, at the time of driving the printer;

FIG. 13 is a top view illustrating the drive transmission mechanism of the thermal transfer printer according to the first embodiment of the invention, which is shown in FIG. 10, at the time of driving the printer;

FIG. 14 is a cross-sectional view taken along line 600-600 in FIG. 9;

FIG. 15 is a cross-sectional view taken along line 700-700 in FIG. 9;

FIG. 16 is a perspective view illustrating a conventional thermal transfer printer;

FIG. 17 is a side view illustrating a drive transmission mechanism of the conventional thermal transfer printer shown in FIG. 16;

FIG. 18 is a top view illustrating the drive transmission mechanism of the conventional thermal transfer printer shown in FIG. 16; and

FIG. 19 is a cross-sectional view taken along line 800-800 in FIG. 17.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the invention are described with reference to the accompanying drawings.

First Embodiment

FIG. 1 is a perspective view illustrating a thermal transfer printer according to a first embodiment. FIGS. 2 to 4 are views illustrating the thermal transfer printer according to the first embodiment of the invention. First, the structure of a thermal transfer printer 1 according to the first embodiment of the invention is described hereinbelow by referring to FIGS. 1 to 4.

As shown in FIG. 1, the thermal transfer printer 1 according to the first embodiment of the invention has a metallic frame 10, a thermal transfer film accommodating member 11, a sheet feeding roller 12, a motor bracket 14 to which a motor 13 is attached, a film take-up member 15, a sheet feeding roller gear 16, plural intermediate gears 17, a metallic conveying roller 20, a resin conveying roller gear 30 connected to an end portion of the conveying roller 20, and a resin intermediate gear 40 for rotating the conveying roller gear 30. Further, as shown in FIGS. 2 to 4, the thermal transfer printer 1 according to the first embodiment of the invention has a resin drive transmission gear 50, which is connected to a drive shaft 13 a of the motor 13, for rotating the intermediate gear 40, and an intermediate gear support shaft 60 rotatably supporting the intermediate gear 40. Incidentally, the thermal transfer printer 1 is an example of the “printer apparatus” of the invention. The conveying roller gear 30 is an example of the “first gear” of the invention. The intermediate gear 40 is an example of the “second gear”. Further, the drive transmission gear 50 is an example of the “third gear” of the invention. The intermediate gear supporting shaft 60 is an example of the “second gear supporting shaft” of the invention.

As shown in FIG. 1, the frame 10 is U-shaped. The thermal transfer film accommodating member 11 and the sheet feeding roller 12 are disposed on the inner surface side of the frame 10. Moreover, the motor 13 transmits a driving force to the drive transmission gear 50 through the drive shaft 13 a of the motor 13. Furthermore, the motor bracket 14 is mounted on the outer surface of the frame 10. Additionally, the film take-up member 15, the sheet feeding roller gear 16, and the plural intermediate gears 17 are placed between the frame 10 and the motor bracket 14. These plural intermediate gears 17 are placed so that the film take-up member 15 and the sheet feeding roller gear 16 can be driven by the single motor 13. Further, as shown in FIGS. 1 and 4, the conveying roller 20 is disposed under the thermal transfer film accommodating member 11 on the inner surface side of the frame 10, and rotatably mounted on the frame 10 by a bearing 18. As shown in FIGS. 2 and 4, a D-cut part 21 is formed in an end portion of this conveying roller 20 by performing a cutting work operation or the like. Furthermore, a D-shaped through hole 31, through which the D-cut part 21 of the conveying roller 20 is inserted, is formed in the conveying roller gear 30.

The intermediate gear 40 has a circular shaft insertion hole 41. Moreover, as shown in FIG. 2, the intermediate gear 40 includes a small-diameter intermediate gear portion 42, which meshes with the conveying roller gear 30, and a large-diameter intermediate gear portion 43 that meshes with the drive transmission gear 50 and that has a diameter, which is larger than that of the small diameter intermediate gear portion 42. Incidentally, the small-diameter intermediate gear portion 42 is an example of each of the “first-side intermediate gear portion” and the “second first-side gear portion”. The large-diameter intermediate gear portion 43 is an example of each of the “second-side intermediate gear portion” and the “second second-side gear portion”. Furthermore, as shown in FIG. 4, the intermediate gear supporting shaft 60 includes an attaching portion 61 fixedly attached to the frame 10 by performing a caulking operation or the like.

Incidentally, in the first embodiment, as shown in FIGS. 2 to 4, the intermediate gear supporting shaft 60 is configured in such a manner as to rotatably support a shaft insertion hole 41 of the intermediate gear 40 and as to provide a predetermined fitting clearance (about 0.2 mm in the first embodiment) between the shaft 60 and the shaft insertion hole 41. Further, a conveying roller gear circular portion 32 having a diameter, which is substantially equal to the reference pitch circle diameter of the conveying roller gear 30, is formed integrally with the resin conveying roller gear 30. Incidentally, the conveying roller gear circular portion 32 is an example of the “first circular portion”. Furthermore, in the resin intermediate gear 40, a small-diameter intermediate gear circular portion 44 having a diameter, which is substantially equal to the reference pitch circle diameter of the small-diameter intermediate gear portion 42, is provided integrally with the small-diameter intermediate gear portion 42. Incidentally, the small-diameter intermediate gear circular portion 44 is an example of each of the “first-side intermediate gear circular portion” and the “second first-side circular portion”.

Further, in the case of the first embodiment, in the resin intermediate gear 40, a large-diameter intermediate gear circular portion 45 having a diameter, which is substantially equal to the reference pitch circle diameter of the large-diameter intermediate gear portion 43, is provided integrally with the large-diameter intermediate gear portion 43. Incidentally, the large-diameter intermediate gear circular portion 45 is an example of each of the “second-side intermediate gear circular portion” and the “second second-side circular portion”. Furthermore, a drive transmission gear circular portion 51 having a diameter, which is substantially equal to the reference pitch circle diameter of the drive transmission gear 50, is provided integrally with the drive transmission gear 50. Incidentally, the drive transmission gear circular portion 51 is an example of the “third circular portion”. Additionally, the conveying roller gear circular portion 32 is disposed so that when the gears are driven, the conveying roller gear circular portion 32 is in contact with the small-diameter intermediate circular portion 44. Further, the drive transmission gear circular portion 51 is disposed so that when the gears are driven, the drive transmission gear circular portion 51 is in contact with the large-diameter intermediate gear circular portion 45.

FIGS. 5 to 8 are views illustrating the drive transmission mechanism at the time of driving the thermal transfer printer according to the first embodiment of the invention, which is shown in FIG. 1. Next, a drive transmission operation of the thermal transfer printer 1 according to the first embodiment of the invention is described hereinbelow by referring to FIGS. 2 to 8.

First, as shown in FIGS. 2 to 4, before the gears are driven, the conveying roller gear circular portion 32 and the small-diameter intermediate gear circular portion 44 are not in contact with each other. Also, the drive transmission gear circular portion 51 and the large-diameter intermediate gear circular portion 45 are not in contact with each other. When the motor 13 is energized in this state, a driving force of the motor 13 is transmitted to the drive transmission gear 50 through the drive shaft 13 a of the motor 13. Thus, the drive transmission gear 50 rotates in the direction of an arrow A shown in FIG. 5. Subsequently, the driving force of the drive transmission gear 50 is transmitted to the large-diameter intermediate gear portion 43 of the intermediate gear 40. Thus, the large-diameter gear portion 43 and the small-diameter intermediate gear portion 44 rotate in the direction of an arrow B shown in FIG. 5. At that time, a force pushing the large-diameter intermediate gear portion 43 in the direction of an arrow D shown in FIG. 5, which is caused due to the driving force transmitted from the drive transmission gear 50, is exerted on the large-diameter intermediate gear portion 43 of the intermediate gear 40.

Subsequently, the driving force of the small-diameter intermediate gear portion 42 is transmitted to the conveying roller gear 30. Thus, the conveying roller gear 30 rotates in the direction of an arrow C of FIG. 5. Consequently, the driving force is transmitted to the conveying roller 20 through the D-cut part 21 of the conveying roller 20, which is inserted into the D-shaped through hole 31 of the conveying roller gear 30. Thus, the conveying roller 20 rotates. At that time, a force pushing the small-diameter intermediate gear portion 42 in the direction of an arrow E shown in FIG. 5 and originating from a force of the conveying roller gear 30 that is always forced by a load, which is caused by the conveying roller 20 and soon, to stop, is exerted on the small-diameter intermediate gear portion 42 of the intermediate gear 40. Thus, when the gears are driven, a force, which is synthesized from a force acting in the direction of the arrow D shown in FIG. 5 and a force acting in the direction of the arrow E shown in FIG. 5 and pushes the intermediate gear 40 in the direction of an arrow F shown in FIG. 5, is exerted on the intermediate gear 40. Consequently, the intermediate gear 40 moves (or swings) in the direction of the arrow F shown in FIG. 5 by the fitting clearance (about 0.2 mm) from the intermediate gear supporting shaft 60 to the shaft insertion hole 41 of the intermediate gear 40 and bites into the conveying roller gear 30 and the drive transmission gear 50. Thus, when the gears are driven, the conveying roller gear circular portion 32 and the small-diameter gear circular portion 44 are brought into contact with each other and rotate, while the drive transmission gear circular portion 51 and the large-diameter gear circular portion 45 are put into contact with each other and rotate.

As described above, in the first embodiment, the conveying roller gear circular portion 32 having a diameter, which is substantially equal to the reference pitch circle diameter of the conveying roller gear 30, is provided on the conveying roller gear 30. Also, the small-diameter intermediate gear circular portion 44 having a diameter, which is substantially equal to the reference pitch circle diameter of the small-diameter intermediate gear portion 42 of the intermediate gear 40, is provided on the small-diameter intermediate gear portion 42 of the intermediate gear 40, which rotates the conveying roller gear 30. Thus, when the gears are driven, the conveying roller gear circular portion 32 and the small-diameter intermediate gear circular portion 44 are in contact with each other. Consequently, the conveying roller gear 30 and the small-diameter intermediate gear portion 42 of the intermediate gear 40 can be meshed with each other so that a part at the side of conveying roller gear 30, which has a diameter being equal to the reference pitch circle diameter thereof, is in contact with a part at the side of the small-diameter intermediate gear portion 42, which has a diameter being equal to the reference pitch circle diameter thereof. Thus, even when at least one of the conveying roller gear 30 and the small-diameter intermediate gear portion 42 of the intermediate gear 40 is eccentric, each of the conveying roller gear 30 and the intermediate gear 40 can be rotated at a constant rotational speed without causing unevenness in the rotation thereof.

Further, in the first embodiment, the large-diameter intermediate gear circular portion 45 having a diameter, which is substantially equal to the reference pitch circle diameter of the large-diameter intermediate gear portion 43 of the intermediate gear 40, is provided on the large-diameter intermediate gear portion 43 of the intermediate gear 40. Also, the drive transmission gear circular portion 51 having a diameter, which is substantially equal to the reference pitch circle diameter of the drive transmission gear 50, is provided on the drive transmission gear 50 that rotates the intermediate gear 40. Thus, when the gears are driven, the large-diameter intermediate gear portion 43 of the intermediate gear 40 and the drive transmission gear 50 are in contact with each other. Consequently, the large-diameter intermediate gear portion 43 of the intermediate gear 40 and the drive transmission gear 50 can be meshed with each other so that a part at the side of the large-diameter intermediate gear portion 43, which has a diameter being equal to the reference pitch circle diameter thereof, is in contact with a part at the side of the drive transmission gear 50, which has a diameter being equal to the reference pitch circle diameter thereof. Thus, even when at least one of the large-diameter intermediate gear portion 43 of the intermediate gear 40 and the drive transmission gear 50 is eccentric, each of the intermediate gear 40 and the drive transmission gear 50 can be rotated at a constant rotational speed without causing unevenness in the rotation thereof.

Furthermore, in the first embodiment, the conveying roller gear circular portion 32 is provided integrally with the conveying roller gear 30, while the small-diameter intermediate gear circular portion 44 is provided integrally with the small-diameter intermediate gear portion 42 of the intermediate gear 40. Thus, even when the conveying roller gear circular portion 32 and the small-diameter intermediate gear circular portion 44 are provided therein, the number of components does not increase. Consequently, the conveying roller gear 30 and the intermediate gear 40 can be rotated at a constant rotational speed without increasing the number of components.

Additionally, in the first embodiment, the large-diameter intermediate gear circular portion 45 is provided integrally with the large-diameter intermediate gear portion 42 of the intermediate gear 40, while the drive transmission gear circular portion 51 is provided integrally with the drive transmission gear 50. Thus, even when the large-diameter intermediate gear circular portion 45 and the drive transmission gear circular portion 51 are provided therein, the number of components does not increase. Consequently, the intermediate gear 40 and the drive transmission gear 50 can be rotated at a constant rotational speed without increasing the number of components.

Further, in the first embodiment, the intermediate gear supporting shaft 60 is mounted in such a way as to provide the predetermined fitting clearance (about 0.2 mm) between the intermediate gear supporting shaft 60 and the shaft insertion hole 41 of the intermediate gear 40. Thus, when the gears are driven, the intermediate gear 40 can easily be moved in such a manner as to bite into the conveying roller gear 30 and the drive transmission gear 50. Consequently, the conveying roller gear circular portion 32 can reliably be in contact with the large-diameter intermediate gear circular portion 45, while the small-diameter intermediate gear circular portion 44 can reliably be in contact with the drive transmission gear circular portion 51. Thus, the conveying roller gear 30 can reliably be meshed with the intermediate gear 40, without separately providing a mechanism for swinging (or moving) the intermediate gear 40, so that a part at the side of the conveying roller gear 30, which has a diameter being equal to the reference pitch circle diameter thereof, is in contact with a part at the side of the intermediate gear 40, which has a diameter being equal to the reference pitch circle diameter thereof. Also, the drive transmission gear 50 can reliably be meshed with the intermediate gear 40, without separately providing a mechanism for swinging (or moving) the intermediate gear 40, so that a part at the side of the drive transmission 50, which has a diameter being equal to the reference pitch circle diameter thereof, is in contact with a part at the side of the intermediate gear 40, which has a diameter being equal to the reference pitch circle diameter thereof.

Further, correction for unevenness in the rotation is performed on the engagement between the drive transmission gear 50 and the intermediate gear 40, in addition to the engagement between the intermediate gear 40 and the conveying roller gear 30. Thus, the unevenness in the rotation, which is caused at the drive transmission gear 50, is corrected at two places. Thus, as compared with a case in which such unevenness in the rotation is corrected at one place, this embodiment can more surely rotate the conveying roller gear 30 at a constant rotational speed.

Second Embodiment

FIGS. 9 to 11 are views illustrating a drive transmission mechanism of the thermal transfer printer according to a second embodiment of the invention. Referring to FIGS. 9 to 11, it is illustrated that this second embodiment has a configuration in which a convex annular portion 41 a is provided in a shaft insertion hole 41 of an intermediate gear 40 a and which constituents respectively corresponding to the large-diameter intermediate gear circular portion 45 of the intermediate gear 40 and the drive transmission gear circular portion 51 of the drive transmission gear 50 of the thermal transfer printer according to the first embodiment of the invention illustrated in FIGS. 2 to 8 are omitted. Incidentally, the remaining constituents of the second embodiment other than the intermediate gear 40 a and the drive transmission gear 50 a are similar to those of the first embodiment.

Concretely, in the second embodiment, the convex annular portion 41 a of the intermediate gear 40 a is formed on a part, which is provided at the side of the frame 10, in the shaft insertion hole 41, as shown in FIG. 11. Further, the annular portion 41 a of the intermediate gear 40 a is formed in such a way as to provide almost no fitting clearance between the annular portion 41 a and the outer periphery of the intermediate gear supporting shaft 60.

FIGS. 12 to 15 are views illustrating the drive transmission mechanism at the time of driving a thermal transfer printer according to the second embodiment of the invention. Next, a drive transmission operation of the thermal transfer printer 70 according to the first embodiment of the invention is described hereinbelow by referring to FIGS. 9 to 15. First, as shown in FIGS. 9 to 11, before the gears are driven, a conveying roller gear circular portion 32 and a small-diameter intermediate gear circular portion 44 are not in contact with each other. When the motor 13 is energized in this state, a driving force of a motor 13 is transmitted to a drive transmission gear 50 a through a drive shaft 13 a of the motor 13. Thus, the drive transmission gear 50 a rotates in the direction of an arrow G shown in FIG. 12. Subsequently, the driving force of the drive transmission gear 50 a is transmitted to a large-diameter intermediate gear portion 43 of the intermediate gear 40 a. Thus, the large-diameter gear portion 43 and the small-diameter intermediate gear portion 44 rotate in the direction of an arrow H shown in FIG. 12. At that time, a force pushing the large-diameter intermediate gear portion 43 in the direction of an arrow J shown in FIG. 12, which is caused due to the driving force transmitted from the drive transmission gear 50 a, is exerted on the large-diameter intermediate gear portion 43 of the intermediate gear 40 a.

Subsequently, the driving force of the small-diameter intermediate gear portion 42 is transmitted to the conveying roller gear 30. Thus, the conveying roller gear 30 rotates in the direction of an arrow I of FIG. 12. Consequently, the driving force is transmitted to the conveying roller 20 through a D-cut part 21 of the conveying roller 20, which is inserted into a D-shaped through hole 31 of the conveying roller gear 30. Thus, the conveying roller 20 rotates. At that time, a force pushing the small-diameter intermediate gear portion 42 in the direction of an arrow K shown in FIG. 12 and originating from a force of the conveying roller gear 30 that is always forced by a load, which is caused by the conveying roller 20 and soon, to stop, is exerted on the small-diameter intermediate gear portion 42 of the intermediate gear 40 a. Thus, when the gears are driven, a force, which is synthesized from a force acting in the direction of the arrow J shown in FIG. 12 and a force acting in the direction of the arrow K shown in FIG. 12 and pushes the intermediate gear 40 a in the direction of an arrow L shown in FIG. 12, is exerted on the intermediate gear 40 a. Consequently, the intermediate gear 40 a moves (or swings) in the direction of the arrow L shown in FIG. 12 by the fitting clearance (about 0.2 mm) from the intermediate gear supporting shaft 60 to the shaft insertion hole 41 of the intermediate gear 40 a. Incidentally, the intermediate gear 40 a is rotatably supported by the intermediate gear supporting shaft 60 on the annular portion 41 a formed in the shaft insertion hole 41 of the intermediate gear 40 a in a state in which there is nearly no fitting clearance. Consequently, the intermediate gear 40 a is inclined and bites into the conveying roller gear 30, as shown in FIG. 15. Thus, when the gears are driven, the conveying roller gear circular portion 32 and the small-diameter gear circular portion 44 are brought into contact with each other and rotate.

Incidentally, advantages of the second embodiment are similar to those of the first embodiment.

Incidentally, it should be understood that the embodiments disclosed herein are illustrative in all respects, and that the invention is not limited thereto. The scope of the invention is defined by the scope of the appended claims rather than by the description of the embodiments. Furthermore, all changes, which fall within the scope of the claims, or equivalence of the scope of the claims, are included by the scope of the invention.

For example, although examples of applying the invention to the thermal transfer printer serving as an example of an apparatus having a drive transmission mechanism have been disclosed in the descriptions of the first and second embodiments, the invention is not limited thereto. The invention is not limited thereto. The invention may be widely applied to apparatuses each having a drive transmission mechanism other than the thermal transfer printer.

Further, although the shaft insertion hole of the intermediate gear and the intermediate gear supporting shaft are circularly cross-sectionally formed in each of the first and second embodiments, the invention is not limited thereto. The shaft insertion hole of the intermediate gear and the intermediate gear supporting shaft may be formed into another shape including an elliptical shape.

Furthermore, although the description of the first and second embodiments have described examples in which the circular portions are provided on one or two sets of the gears meshed with one another when the driving force is transmitted, the invention is not limited thereto. The circular portions may be formed on the gears of three sets or more, which are meshed with one another when the driving force is transmitted. Alternatively, the circular portions may be provided on all the gears of the drive transmission mechanism. 

1. A drive transmission mechanism for a printer apparatus comprising: a metallic conveying roller for conveying sheets; a resin conveying roller gear connected to one end portion of the conveying roller; a resin intermediate gear, provided with a shaft insertion hole, for rotating the conveying roller; a resin drive transmission gear, mounted on a drive shaft of a motor, for rotating the intermediate gear as the motor is driven; and an intermediate gear supporting shaft for rotatably supporting the shaft insertion hole of the intermediate gear, wherein: the intermediate gear includes a first-side intermediate gear portion meshed with the conveying roller gear, and also includes a second-side intermediate portion meshed with the drive transmission gear; the intermediate gear is disposed in a position, in which the intermediate gear is caused by a load of the conveying roller to bite into the conveying roller gear and the drive transmission gear, when the gears are driven; the resin conveying roller gear includes a conveying roller gear circular portion that is provided integrally with the conveying roller gear and that has a diameter being substantially equal to a reference pitch circle diameter of the conveying roller gear; the resin drive transmission gear includes a drive transmission gear circular portion that is provided integrally with the drive transmission gear and that has a diameter being substantially equal to a reference pitch circle diameter of the drive transmission gear; the resin intermediate gear further includes a first-side intermediate gear circular portion, which is provided integrally with the drive transmission gear and has a diameter being substantially equal to a reference pitch circle diameter of the first-side intermediate gear portion, and also includes a second-side intermediate gear circular portion that is provided integrally with the intermediate gear portion and that has a diameter being substantially equal to a reference pitch circle diameter of the second-side intermediate gear portion; the intermediate gear supporting shaft is mounted in the shaft insertion hole of the intermediate gear in such a way as to provide a predetermined fitting clearance between the intermediate gear supporting shaft and the shaft insertion hole; the conveying roller gear circular portion is disposed in such a way as to be in contact with the first-side intermediate gear circular portion when the gears are driven; and the drive transmission gear circular portion is disposed in such a manner as to be in contact with the second-side intermediate gear circular portion when the gears are driven.
 2. A drive transmission mechanism comprising: a first gear; and a second gear having a second first-side gear portion for rotating the first gear, wherein: the first gear includes a first circular portion that is provided integrally with the first gear and that has a diameter being substantially equal to a reference pitch circle diameter of the first gear; the second gear includes a second first-side circular portion that is provided with the second first-side gear portion and that has a diameter being substantially equal to a reference pitch circle diameter of the second first-side gear portion; and the first circular portion is disposed in such a way as to be in contact with the second first-side circular portion when the gears are driven.
 3. The drive transmission mechanism according to claim 2, further comprising: a shaft insertion hole included the second gear; and a second gear supporting shaft mounted in such a manner as to rotatably support the shaft insertion hole and as to provide a predetermined fitting clearance between the second gear supporting shaft and the shaft insertion hole.
 4. The drive transmission mechanism according to claim 2, further comprising: a third gear for rotating the second gear, wherein the second gear further includes a second second-side gear portion meshed with the third gear, and also includes a second second-side circular portion that is provided integrally with the second second-side gear portion and that has a diameter being substantially equal to a reference pitch circle diameter of the second second-side gear portion; the third gear includes a third circular portion that is provided integrally with the third gear and that has a diameter being substantially equal to a reference pitch circle diameter of the third gear; and the second second-side circular portion is disposed in such a manner as to be in contact with the third circular portion when the gears are driven.
 5. The drive transmission mechanism according to claim 2, wherein the second first-side circular portion is provided integrally with the second first-side gear portion 